Technical Reference for Water

Conservation in Cooling Towers

1st Edition, Nov 2017

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Table of Contents

Preface ........................................................................................................................ ii

Acknowledgements .................................................................................................... iii

Terminology ............................................................................................................... iv

Part 1 General Introduction of Cooling Towers ........................................................ 1

1.1. Overview ....................................................................................................... 1

1.2. Cooling Tower Types .................................................................................... 1

1.3. Guidelines and Regulatory Requirements of Cooling Towers ....................... 5

Part 2 Water Use and Conservation ........................................................................ 6

2.1. Understand the water balance and consumption .......................................... 6

2.2. Water Efficiency Audits and Reporting .......................................................... 8

2.3. Water Quality and Chemical Treatment ........................................................ 8

2.4. Non-chemical Treatment ............................................................................. 12

2.5. Operation and Maintenance ........................................................................ 13

2.6. Factors Limiting the Increase in COC ......................................................... 18

2.7. Using Alternative Water Sources ................................................................ 20

Part 3 Best Available Technology .......................................................................... 22

3.1 Overview ..................................................................................................... 22

Part 4 AirConditioning Condensate Re-Use ........................................................ 24

4.1 Introduction ................................................................................................. 24

4.2 Typical condensate recovery and re-use system ........................................ 24

4.3 Components required for collection of condensate ..................................... 25

References ............................................................................................................... 26

Annex A Cooling Tower Water Balance ................................................................ 27

Annex B Cooling Tower Water Saving Checklist ................................................... 30

Annex C - Typical Parameters of Potable Water, NEWater and Industrial Water as

Makeup Water for Cooling Tower ............................................................................. 32

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Preface

In hot and humid Singapore, water-cooled chillers are one of the ways to keep buildings cool for its occupants. The air-conditioning systems rely mostly on wet / evaporative cooling towers (smaller percentage on air cooled towers) that eject heat from the building by evaporating water. Even manufacturing plants and industrial plants adopt these cooling towers to meet the cooling demand of their processes. Although cooling towers are the best available technology to meet cooling demand, competing forces such as drought conditions, growing population and increasing water demand for various uses are diminishing the water availability in Singapore.

Every day a significant amount of energy is also wasted in the form of water and waste heat from air-conditioning and evaporative cooling systems. It is estimated that more than 30 mgd (million gallons per day) of water is used by evaporative cooling towers in Singapore. Reducing that water demand and saving energy in the process is a matter of PUBs interest to stem further water losses to the atmosphere and instil water conservation among users.

The aim of this technical guide is to provide cooling tower users, developers, building owners and managing agents with a basic knowledge of cooling tower management, and proper operation and maintenance of these equipment in their premises. By adopting this set of guidelines, PUB hopes to instil discipline and equip users on the technical knowhow for the management of these devises to maximise water savings i.e. optimise the cycles of concentration, while still meeting cooling demands for buildings or industrial processes. The topics covered seek to address concerns on the existing requirements for control of scale, corrosion, deposition and biological fouling associated with the operation of a cooling tower water system. In addition, increased efficiency in the use of energy and control of both makeup water and discharge of residual concentrate will be highlighted as well as health and safety hazards, environmental challenges, and non-chemical systems.

This technical guide should be read in conjunction with the relevant codes of practice and guidelines issued by the National Environment Agency, and the Environmental Public Health (Cooling Towers and Water Fountains) Regulations.

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Acknowledgements

The advice, comments and contributions of the following government agencies, professional bodies, consultants, private entities and academics are gratefully acknowledged:

Alex Wong, Director, Excel Consultant and Services Pte Ltd

Alven Yee, Water and Process Technologies, GE Power

Grace Cheok-Chan, Principal Manager, Building and Construction Authority

Professor Lee Poh Seng, Department of Mechanical Engineering, National University of Singapore

Dr Louis Hong Kar Cherng, Senior Technologist, Ecospec

Patrick Lim, Senior Manager, Kurita

Dr Pranav S. Joshi, Senior Assistant Director (Drinking Water Unit), Food &

Environmental Hygiene Department, National Environment Agency

Pok Kwoon Yong, Assistant Manager (Drinking Water Unit), Food & Environmental Hygiene Department, National Environment Agency

San Linn Nyunt, Manager, Kurita

Sumalya Nag, Senior Sales Operation Director, Water and Process Technologies, GE Power

Tan Vui Chee, Marketing Director, NALCO Water

Tany Tay, Senior General Manager, Ecospec

Dr Zhang Kai, Industry Technical Consultant, NALCO Water

Dr Zhao Xijing, Senior Manager, Building and Construction Authority

Disclaimer: The ideas presented in the document are not intended as an endorsement

by PUB of any particular method, process or product.

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Terminology

Biocide A chemical capable of killing or inactivating living microorganisms.

Bleed off (Blowdown)

Water deliberately discharged from a cooling system to control the concentration of dissolved solids.

Cooling tower Any device in which atmospheric air is passed through sprayed water in order to lower the temperature of the water by evaporative cooling.

Corrosion An electrochemical process in which metals are oxidized by transferring electrons from an anodic site to a cathodic site.

Corrosion inhibitors

Chemicals that can prevent or slow down the waterside corrosion of metals.

Cycles of concentration

The theoretical number of times water circulates within the cooling system before being discharged via blowdown. This theoretical number can be calculated by various hydraulic and composition means, but should arrive at the same value.

Drift Water aerosol, which emerges from the airflow outlet of a cooling tower.

Drift eliminator Any device or physical barriers, designed to minimize the drift emanating from the cooling tower.

Fill The medium used in cooling towers to increase the surface area of the tower.

Fouling Organic growth or other deposits on heat transfer surfaces causing loss of efficiency.

Forced Draft Counter Flow

A type of cooling tower that air is forced upward through the water falling from the top of the tower to the basin.

Forced Draft Cross Flow

A type of cooling tower that air is forced across the water falling from the top of the tower to the basin.

Induced Draft Counter Flow

A type of cooling tower that air is drawn or induced in the opposite direction to which the water is falling.

Induced Draft Cross Flow

A type of cooling tower that air is drawn or induced across the water falling from the top of the tower to the basin.

Legionella A genus of bacterium which is ubiquitous in aqueous environments and found in water systems in the built environment, including cooling systems that are not properly or

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regularly maintained. It comprises numerous species. Legionella pneumophila is the most common causative organism of legionnaires disease.

Makeup water Water added to cooling tower basin to replace water loss by

evaporation, bleed, drift, splash and overflow.

Scale A hard deposit that is formed on surfaces by the precipitation of

mineral particles in water.

Scale inhibitor Chemicals that prevent scale formation by dispersing the scale forming minerals or modifying the crystal structure of scale.

Splash out Water leaving the tower via the air intakes and other openings in the tower casing.

Variable speed drive

A way of controlling the speed of a motor, usually electronically using an inverter. The speed can be varied manually, but is more often controlled